Why it matters: This year’s results show that nitrate level recommendations for side-dressing and top-dressing may vary for corn growers across the province, depending on when they were able to get their crop planted.

The OMAFRA field crop team completed samples from 66 different sites across Ontario from June 17 to June 19 at a V3 to V4 stage target this spring as part of its yearly test survey.

Jake Munroe.photo: Supplied

“We collected different sites across the province, we took zero to 12-inch depth soil samples and sent them to the lab for nitrate analysis,” says Jake Munroe, soil specialist with OMAFRA.

The nitrate soil values came back 8.5 to nine ppm, three to 3.5 parts lower than the long term average of 12 ppm.

Dale Cowan, senior agronomist and sales manager with Agris Co-op, found the same results with tests he had taken this year – that showed a need for a 40-pound increase in nitrogen recommendations.

Neither Cowan nor Munroe are surprised by these results as the cooler temperatures Ontario has experienced this spring led to less mineralization – the process of organic material being broken down to inorganic material, nitrogen into nitrate – within the soil throughout all soil types. As well, heavier textured soils have the possibility of added denitrification due to excessive saturation.

Dale Cowan.photo: Supplied

“It isn’t surprising when you think of about 210 heat units behind, our average daily temperature is 2.7 degrees Celsius less since May 1 and we have had anywhere from 30 to 80 per cent more rain than normal,” says Cowan. “We’ve lost six to seven weeks of mineralization since April 1, and in my experience we don’t make up for [that] later.”

Although the nitrate levels in the soil are lower, farmers who were late planting will still be aiming to apply approximately the same amount of nitrogen as they have in previous years as side-dress or top-dress application.

“Our yield potential may be down slightly but also our soil supply is low. These two just may cancel each other out and we end up putting the same rate of nitrogen on that we did last year,” says Cowan.

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For growers who had the opportunity to get corn planted earlier, the recommendation could be different.

“For growers with earlier planted corn, with a good stand and good yield expectation, they may want to consider slightly bumping up their rates as the crop is advancing much ahead of the rest of the province,” says Munroe.

Cowan and Munroe remind farmers that these results are general guidelines and it’s very important for growers to head out to their fields and check their nitrate samples.

“Look at the plant population, uniformity, emergence, planting date, yield potential, soil conditions etc. and base your yield goals and nitrogen recommendations on what you see in those fields,” says Cowan.

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Nitrate soil sampling

OMAFRA guidelines on how to collect a nitrate soil sample:

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Collect several 12-inch soil samples across a field with a soil probe.

It is important to sample parts of the fields separately, especially if there are reasons to suspect different nitrogen contents, such as history, soil type and topography.

Make a well-mixed representative sub sample of approximately one lb. to fill a lab bag or box.

Be sure to chill samples, preventing further mineralization and send to a lab as soon as possible.